TDI Engine 1Z: Specs, Problems & Solutions

Hello everyone.
I've owned a Passat 35i TDI Variant with engine code 1Z since 1996.
Current mileage: 184,600 km.
For a few weeks now, the engine has been acting up:
On the highway (although I mostly drive in the city), the engine loses power from around 140 km/h.
'If I then release the accelerator, I can accelerate up to about 160 km/h afterwards. However, even then, you don't really feel any power.'
When I let off the gas, it takes forever for him to get back up to speed.

Around the same time, the following also occurred:
The vehicle simply turns off while driving or even when it's stopped.
Then it's like the ignition is turned off.
When restarting the system immediately (sometimes while driving), it reappears right away. Once, it didn't reappear until about 3 minutes later.

For about three weeks now, another phenomenon has been added to the list:
The engine speed is not behaving as the accelerator pedal indicates.
Sometimes the idle speed remains at around 1300 RPM, or the vehicle unexpectedly accelerates, which has been quite severe before because I was braking at that moment!

The error memory indicates something like 'intermittent implausible signal at the throttle position sensor' or similar.

Since the error doesn't occur constantly, I'm not sure what to make of it.
I also suspect that a badger might have been inside, because the engine compartment is dirty, but an inspection of the cables (visual check) showed no damage.

'About two weeks ago, I inspected the intake system because I had read about issues with the exhaust gas recirculation (EGR) and soot buildup in the intake manifold. During the inspection, I noticed a significant oil film in the area between the air filter housing (LF) and the intercooler (LLK), and also between the intercooler and the engine. I cleaned the rubber hoses and reassembled everything.'

Since I'm not very familiar with diesel engines, I need your help.

The guys at VW are also facing a puzzle.

Best regards.
Sure, here is the translation of the text from German to English:

'Micha' translates to 'Michael' in English.

Hello,

Have you had the throttle position sensor and wiring checked due to the error message? If so, do you still have the measured values?

Hello Micha.
Since the error only occurred sporadically until my last visit to Volkswagen, and Uwe was incredibly busy, we postponed troubleshooting until it becomes more 'troublesome.'

But I have a question: What is the likely amount of effort required for measuring it? Could I possibly do it myself with a multimeter?
Bitte gib mir den deutschen Text, den du übersetzt haben möchtest.
Here's another piece of information regarding the phenomenon with the performance drop:
Around 3000 RPM, I tested it again today, the power suddenly drops (to about 75%, if I had to guess **wink**). If you keep your foot on the accelerator, there's more power again around 4200 RPM.

'Furthermore, the following:'

If I drive gently and don't demand strong acceleration, the gas pedal behaves normally.
If I accelerate a bit more, I experience a significant 'load change' when shifting gears. The engine RPM initially increases when releasing the clutch, then drops sharply, and for about half a second, the power almost completely disappears (it feels almost like braking), before slowly increasing again.
In this context, the high idle speed of approximately 1300-1500 RPM then occurs (e.g., at the next traffic light). This can be reduced to around 875 RPM by gently pressing the accelerator or slipping the clutch, and it will then remain at that level.

It seems that this is not just a problem, or is it?

I also experienced my Passat turning off while driving; this problem occurred more and more frequently. In my case, the engine control unit (ECU) for the immobilizer was defective, so I replaced it with a new one, and since then it has been working properly again.

Regards,
*Mario

Hello,

Why don't you also do a measurement run? The values for cylinder 1 are in the error database.
Please also check block 2, field 2 (throttle position) in the engine control unit (ECU).
When the pedal is not pressed, the value should be 0%. When the pedal is fully depressed, the value should be 100%. There should be no sudden jumps in the value when the pedal is slowly pressed.

Hello Micha.
If I understand correctly, I need to...
such a test drive, whether it's the much-hyped...
VAG COM or assistance from Volkswagen?

Regards,
Sure, here is the translation of the text from German to English:

'Micha' translates to 'Michael' in English.

Hi.

... could be caused by anything from a faulty pedal position sensor, in my opinion.

Based on experience, different symptoms often have only one underlying cause, and in this case, it's likely that a driver who is "erratically but thoroughly" pressing the accelerator pedal is to blame for everything.
It can also cause a performance drop, as the engine will enter emergency mode if it receives implausible signals from the sensor.

Hi Ulf.
Am I correct in assuming that the engine can only be taken out of emergency mode by...?
Does turning the ignition off and on again bring it back, or am I mistaken?
I'm asking because I've been experiencing these performance drops.
I mean, at least, it always happens within a specific RPM range...
and then he drives normally either above or below it.


but it already sounds very plausible...
It wouldn't be that financially burdensome, would it?

Best regards.
micha

micha_passat wrote:

Am I correct in assuming that the engine only returns from limp mode by turning the ignition off and on, or am I mistaken about that? I'm asking because I've been experiencing these performance drops. I mean, at least, it always happens within a specific RPM range... and then he drives normally either above or below it.

Hi Micha,

As far as I know, the emergency behavior also depends on the generation.

Newer models can probably only be reset by turning off the engine.
Older systems disable the emergency stop as soon as the cause (implausible input values) disappears – although I'm not entirely sure about that.

If I'm correct, your 1994 model would likely be considered one of the older versions, and the issue could still be explained by the accelerator pedal.

Given the mileage, a faulty sensor might not be the obvious cause of the problem (especially since, based on general experience, it doesn't seem to be a predictable point of failure), but I still think it's possible.
Especially since the error database also contains a note about a series of "susceptible" accelerator pedals.

Regarding the price: don't get too excited yet - unfortunately, most things related to TDIs are more expensive than you might initially think.
I don't have any more specific information about the pedal.

Especially since the error database also contains a note about a series of 'vulnerable' accelerator pedals.
Hi Ulf.
How did you find this clue?
Am I just too stupid?

Sure, here is the translation of the text from German to English:

'Hello.'
Sure, here is the translation of the text from German to English:

'Micha' translates to 'Michael' in English.

Hello,

Check out the section titled "Documentation for A4, Emergency mode after strong acceleration."

I have a G4 from 11/98 with a 110 horsepower TDI engine.
Approximately one year ago, I experienced similar issues to what mika_passat described.
The problem was actually the accelerator pedal: The value when the pedal was fully depressed was significantly above 100%, which caused the engine to simply shut off under full load (full throttle and high RPM). This is quite something, especially at around 200 km/h!

Changing the pedal then provided a solution.

Changing the pedal :then provided a solution.
Pedal? or sensor?
I thought that was two different things?

micha_passat wrote:

tito wrote: Changing the pedal :then provided a solution. Pedal? or sensor? I thought that was two different things?

The pedal can of course remain in place (as long as it is not bent or damaged in any way). The part that is important for the Electronic Stability Control (EDC) is the pedal sensor .

I thought so too...

Hi, it's me again.
After a while of ':lol:coming to terms with the fact that the key wasn't working so well,' I asked a good friend who works at VW last week to take a look and replace the timing belt at the same time.
He initially found that there were no error codes stored in the system's memory.
Then he checked all the cables and tested the accelerator pedal sensor (as much as possible), but found nothing there either.

With the new timing belt, the car initially feels much better to drive.
He has more pressure again... My friend told me that when he changed it, he noticed the belt was very loose. It was about time (but actually, the belt had only been in for 105,000 miles, and I'm now at 185,000).
Well, I experienced the effect several times where the car simply turned off while driving. Turning the ignition on and off, and the engine would immediately start again.
Now, on Friday, I had a key experience: I parked the car, went to quickly get something, and then tried to leave... but no luck: nothing happened... no ignition.
It wasn't until after some knocking under the dashboard that I saw a notification again.
So, yesterday I removed the immobilizer (anti-theft system) and inspected it for loose connections. It's located behind the headlight switch on the left side of the interior paneling of the dashboard, and you have to really contort yourself and use a flexible screwdriver shaft to get it out.
I was able to spot a loose connection with the naked eye on the circuit board, specifically at one of the two large relays.
It was quickly resoldered and reinstalled. (Volkswagen would have replaced the entire unit for 300 euros, plus readjusting the module to the key transponder and other things.)
... unfortunately, I only had time for a short test drive, during which no further malfunctions occurred.
I will continue to report here on whether the remaining part also dissolves into thin air?